Generally speaking, a paper machine is made up of three sections, namely the forming section, press section and dryer section. In each section an endless engineered fabric is used to transport a continuous paper sheet through the paper machine. The structure of the fabrics for each section differs, as the functions of each section of the paper machine are different.
The fiber suspension is discharged in a fine, even, cross-machine stream onto a porous wire in the forming section, typically known as a fourdrinier wire. Water drains via gravity through the wire from the fiber suspension. A press fabric for the press section must be capable of rapidly absorbing and expelling water while supporting the newly formed paper sheet. By the time the paper web enters the drying section from the press section as much as fifty percent of the water has been removed from the web. The remaining water removal is completed in the dryer section. The paper web is carried by dryer fabrics transferring the web in succession to rotating dryer cylinders arranged along the length of the dryer section and is heated by high pressure steam circulated within the dryer cylinders.
Endless woven fabrics as described above require special weaving looms, making the fabrics costly and slow to manufacture. The ends of the fabric are joined together using, e.g., thermoplastic welding; however, joining by thermoplastic welding may be unreliable, has a relatively high rate of failure, may result in a weak joint, has poor wear resistance, and has poor caliper and porosity variation. If the fabric ends are “butted” together, the join area is prone to gap open as the felt elongates, or stretches, on the paper machine during use.
U.S. Pat. No. 5,731,063 (Schultz et al.) discloses a paper making felt and substrate which is bonded together with a fuse bonded joint using ultrasonic welding. Referring to FIG. 8, the ends of a substrate are clamped between stabilizing strips 64, and ultrasonic welder 75 welds the ends together. The heat generated by the ultrasonic welding renders the substrate substantially impermeable in the joint area.
PCT/GB89/00681 discloses a method for manufacturing a fabric for use in a paper making machine, wherein free ends 12, 13 of fabric 11 are folded over, butted together, and then sewn to the adjacent portion of the fabric (FIG. 2). The loops 17, 18 at the opposite ends of the fabric created by folding ends 12, 13 are joined together by inserting a pintle wire 19 through the loops 17, 18. Pintle wire 19 of course increases the physical size of the fabric in the join area.
What is needed in the art is a method and corresponding apparatus for joining ends of a fabric together which is simple, reliable and cost effective.